The amount of detail is enough to show why my access point is unable to join the controller. The discovery request was received on the wrong VLAN, the native VLAN, while my controller management and AP manager sit on VLAN 10. The controller drops the packet and we have an error.

The fix was to place the access point on the correct VLAN on the switch port. An example configuration for that switch port:

In summary, to troubleshoot AP joining issues we must start with the basics. Ensure the AP has IP connectivity and can reach the controller. If more troubleshooting is required, utilize available debug commands to find out the reason for the AP not being able to join the controller.